This invention relates to an inlay of a dental component, in particular a dental abutment, for use in combination with a dental implant. The component consists of the inlay, which in use connects the component to the implant, and another part for carrying out the main function of the component, for example supporting a dental prosthesis. The two parts are in use fixed together and may be constructed of different materials.
Dental implants are used to replace individual teeth or for anchoring more complex structures, which generally replace several or even all of the teeth. The materials used for dental implants are often titanium and alloys thereof. These materials have the necessary strength for withstanding the mechanical loads that occur, and they are at the same time sufficiently biocompatible for osseointegration and long term use in the mouth.
Implants have two essential parts: an anchoring part and an abutment part. The anchoring part is embedded in the bone, where it osseointegrates with the bone tissue to provide a firm anchor for the prosthesis. The abutment extends into the oral cavity and provides a support for the prosthesis. The desired prosthetic element (e.g. bridge or crown) is fastened over the abutment such that at least part of the abutment is housed within the prosthesis and provides core support to this. The prosthetic element can be adhesively bonded, cemented, screwed or directly veneered onto the abutment.
The implant can be constructed in one part, such that the anchoring part and abutment part are produced in one integral piece. Hence in such implant systems the integrated anchoring part and abutment are always positioned within the mouth at the same time and the single piece implant extends through the soft tissue into the oral cavity to form a core support for the prosthesis.
However, implants are also often constructed in two or more parts, in which case they consist of at least an anchoring component, often referred to in isolation as the implant, and a separate abutment, sometimes referred to as a spacer. The anchoring component is usually either embedded completely in the bone, that is to say to the height of the alveolar crest, or protrudes by a few millimeters from the alveolar crest into the soft tissue. The abutment is mounted either directly or indirectly to the anchoring component after the latter has become incorporated (osseointegrated) into the bone or directly after the anchoring component has been inserted. It can also be attached to the anchoring component prior to insertion. Most usually the abutment is not mounted until after osseointegration. In such cases a component called a healing cap is often mounted to the implant during the osseointegration process to prevent incursion of soft tissue over the implant site.
In contrast to one piece implants, multi-part implants are more versatile, because the anchoring part and the abutment can be adapted to individual requirements. In particular the abutment shape and angulation, relative to the anchoring part, can be selected after implant insertion. This provides the surgeon with more flexibility and room for error in the placement of the implant. An additional advantage of multi-part implants is that the abutment can be made from a different material than the anchoring part.
Due to their versatility multi-part and particularly two-part dental implants are more commonly used than one-piece implants, and it is this form of implant system with which the present invention is concerned. For the remainder of this specification therefore, the term “implant” will be used to denote the anchoring component of a multi-part implant, namely, the element which in use is anchored within the bone but which does not directly provide core support to the final prosthesis, and the term “secondary component” will be used to denote a component which is, in use, directly or indirectly fastened to the implant. The secondary component can be an abutment, which in use extends into the oral cavity and provides core support for a dental prosthesis, and thus forms a part of the complete implant, or in some instances may comprise an auxiliary component which is temporarily fixed to the implant, such as a healing cap.
As mentioned above, one advantage of multi-part implants is that the abutment can be made of a different material than the implant. Although titanium and its alloys possess many qualities that make these materials particularly suited for dental implants, one large disadvantage is their colouring. It is a relatively common occurrence that, after implant placement, some bone absorption (bone loss) occurs, which leads to a corresponding displacement of the gingiva and the exposure of the implant structure, including parts of the abutment. The grey, metallic colour of titanium means that any such exposure is noticeable and unsightly. In addition, when the abutment is made of metal the covering prosthesis must be opaque enough to prevent any metal colouring from showing through the prosthesis, as this will reduce the natural appearance of the restoration.
In recent years there has been much interest in the use of ceramic materials, such as zirconium dioxide and silicon dioxide, for implant structures including both implants and abutments. Ceramics have the necessary strength and biocompatibility needed and in addition have a white colouring which is more aesthetically pleasing. However, ceramic materials are also more brittle than metals, meaning these are harder to manufacture and consequently more expensive. In addition the use of ceramic implants is still a developing field and the long term success of such implants is not yet known.
In order to combine the aesthetic appeal of ceramics with the functionality and established success of titanium implants, so-called hybrid abutments are known.
These consist of a metal inlay, which comprises connection geometry to enable this to be securely and non-rotationally connected to an implant. Coronal of the connection geometry is a post portion to which a ceramic overlay can be attached, via bonding, moulding, sintering etc. The ceramic overlay thus comprises at its apical end an accommodation cavity in which the post portion of the inlay is housed. The overlay is designed such that, in use, this extends through the soft tissue into the oral cavity to provide support for a dental prosthesis. In this way, the connection between the implant and abutment is metal-to-metal, and thus creates a secure attachment which will not deteriorate over time, while the coronal areas of the abutment are ceramic and hence provide an improved visual appearance.
In accordance with conventional dental terminology, “apical” refers to the direction towards the bone and “coronal” to the direction towards the teeth. Therefore the apical end of a component is the end which, in use, is directed towards the jaw bone and the coronal end is that which is directed towards the oral cavity.
Examples of hybrid abutments are known, for example, from U.S. Pat. No. 5,447,435; EP1269932 and U.S. Pat. No. 5,685,714.
In all such hybrid abutments, it is important to ensure that there is no relative rotation between the inlay and overlay once these have been connected together. In many cases this rotational security is achieved by providing complementary anti-rotation means on the inlay post and in the overlay cavity. Such anti-rotation means must be non-circular symmetrical about the longitudinal axis of the post and cavity, which in use are co-axial. Thus, the anti-rotation means may consist of a section of the post portion and accommodation cavity having complementary oval or polygonal cross-sections, e.g. octagonal. When the octagonal post portion is inserted into the octagonal cavity it is not possible to rotate the inlay relative to the overlay. Alternatively the anti-rotation means may comprise one or more radially extending protrusion on either the post portion or cavity which is arranged to fit within a complementary groove on the cavity or post portion respectively.
It is important that the anti-rotation means of the inlay and overlay fit together snugly, both in order to prevent rotational play and also to ensure that there are no gaps at the external interface of the components, which could form bacteria traps. The creation of precisely connecting anti-rotation means, particularly within a brittle ceramic overlay, can be complex and lead to high manufacturing costs.